Apparatus for maintaing liquid level within a steam and water drum constant



May 1963 A R. MUMFORD APPARATUS FOR MAINTAINING LIQUID LEVEL WITHIN ASTEAM AND WATER DRUM CQNSTANT Filed April 27, 1961 Ma d- ATTORNEY UnitedStates Patent 3,089,469 APPARATUS FOR MAHNTAINING LIQUID LEVEL WITHIN ASTEAM AND WATER DRUM CON- STANT Albert R. Mumford, Bogota, N.J.,assignor to Combustion Engineering, Inc, Windsor, Conm, a corporation ofDelaware Fiied Apr. 27, 1061, Ser. No. 105,936 1 Claim. (Cl. 122-491)This invention relates to apparatus for maintaining the liquid levelwithin a steam and Water drum substantially constant, regardless ofvarying conditions.

In many boilers utilizing a convection bank of steam generating tubes inthe gas outlet pass of a furnace, it is dilficult to maintain a constantwater level within the steam and water drum that supplies these steamgenerating tubes as the load requirements of the boiler change. Prior tothis invention, a load change of 20,000 lbs. of steam per hour in oneparticular instance was accompanied by a water level change within thesteam and water drum of about 16 inches. This greatly varying waterlevel within the drum is highly undesirable. If the water level risestoo high within the drum, it may cause water to carry over into thesuperheater or turbine, depending on the type of boiler employed. A highWater level also reduces the efficiency of the steam and waterseparators normally employed within the drum. Too low a water levelenhances the possibility of steam being generated in the downcomertubes, which would reduce the natural circulation of fluid out of thedrum through the downcomers and back into the drum through the risertubes. With a reduced circula tion through the downeomers and risers,some tubes may become too hot and burn out, requiring shut down of theunit and replacement of such burner out tubes.

It is an object of this invention to enable a substantially constantliquid level Within the steam and water drum to be maintained at alltimes.

When the load requirements of a boiler increase, and more steam leavesthe drum to flow either to the superheater or to the turbine, the amountof feedwater flowing from the economizer to the steam and water drum isalso increased. The temperature of the feedwater being introduced intothe steam and water drum is well below the saturation temperature withinthe boiler. When the subcooled feedwater is thus injected into the drumin large amounts, it will lower the over-all temperature therein, andwill cause condensation of the steam, thus raising the water level.

In accordance with my invention, a substantially vertical baflie whichis parallel to the longitudinal axis of the drum is placed within thedrum, which baffle extends from the bottom of the drum to an upper pointsix to eight inches below the normal liquid level. Depending onconditions, it may in some instances be desirable to extend the baffleto an upper point approximating the normal liquid level. The battleseparates the lower side of the drum where the downcomer tubes areconnected thereto from the rest of the drum internal. Within this areaconfined or segregated by means of the baffle, the feedwater pipeextends. The openings in the feedwater pipe are positioned such that theincoming feedwater is directed towards the area of the drum just abovethe downcomer tube outlets. In this manner the greater portion of thecomparatively subeooled feedwater is restricted to the vicinity of thedowncorner outlets, and hence does not mix with the steam and Waterwithin the drum so as to cause condensation and resultant increase inthe liquid level.

A second advantage of such a construction, and probably the moreimportant advantage, is that by restricting the comparatively coolerfeedwater within the area just above the downcomer tubes, the water thatflows through .these tubes will be at a much lower temperature than itwould otherwise be without utilization of my invention. This lowertemperature increases the density of the water flowing through thedowncomer tubes, and results in a downcomer flow such that no steam willbe generated in the downcomers. In a natural circulation flow, where thedifference in density between the water in the downcomers and themixture of water and steam within the riser tubes is utilized tomaintain circulation, the greater density of the water in the downcomertubes will result in an in creased circulation.

In one boiler unit where the steam and water drum was used both With andwithout my invention, a change in load of 20,000 lbs. of steam per hourbrought about a change in water level within the drum of 16 incheswithout utilizing my invention. With the baflle plate and suitablypositioned openings in the feedwater pipe, a change in load of 100,000lbs. of steam per hour was accompanied by a Water level change of onlyfour inches.

The foregoing will be more readily understood after reading thefollowing description of a preferred embodimerit when considered inconjunction with the accompanying drawings wherein:

FIGURE 1 is a cross-sectional side view of a steam and water drumincorporating my invention;

, omizer (not shown) through pipe 12 which is connected to pipe 14.Water flows in restricted paths from the drum 10 down through the gaspass in the outlet of a furnace by means of rows of downcomer tubes '16which extend along the entire length of the drum 10, and is circulatedback into the drum by means of risers =18 which also extend alongsubstantially the entire length of the drum as shown in FIGURE 2. Amixture of steam and water is returned to the drum through risers 18,after absorbing heat from the hot gases flowing through the furnaceoutlet gas pass. Since the risers tubes are upstream of the downcomertubes in the gas pass, these tubes will be exposed to hotter gases, andhence will absorb more heat, so that steam is formed within these tubes.The difference in density between the water in downcomers 16 and themixture of steam and water in risers 18 sets up a natural circulationflow of fluids therethrough.

The mixture of steam and Water from risers 18 enters the drum 10 and isguided by means of housing 20, which completely surrounds the riserinlets, into ducts 22. Duets 22 direct the high velocity flow of themixture into two rows of separators 24. Brackets 25 may be used to helpsupport the ducts 22 and separator structure. The separators 24 comprisean inner cylinder wall 26 containing fixed vanes or blades 28, whichtend to throw the water contained in the mixture outwardly against theWalls 26, due to centrifugal force created by the shape of the vanes.This separated water continues upwardly along the wall and is directedinto the annular passage between wall 26- and wall 30 by means of uppercurved end 32. The steam flows upwardly in the central part of cylinder26, and leaves the separator through screened hoods 34, where more wateris separated out of the steam. The steam is withdrawn from the drum 10through pipes 38, after first passing through drying means 36, whichconsists of a nurnber of screens. The separated Water falls by means ofgravity to the bottom of the drum, the level of such water beingindicated at 40. Although my invention has been illustrated inconjunction with a drum containing centrif ugal separators, it is to beunderstood that any separating means could be used equally as well.

As mentioned earlier, the temperature of the feedwater entering the drumthrough pipe 14 is at a much lower temperature than the temperature ofthe steam and water within the drum. To confine this cooler feedwater,so as to allow cooler water to flow into the downcomers, and also toprevent its tendency to cause condensation of the steam and ultimaterise in the liquid level, battle 42 is provided. As illustrated, baffle42 extends from the bottom of the drum to a point just below the liquidlevel 43. As mentioned earlier, it may sometimes be desirable to havethe bafile extend up to the normal liquid level. Bafile 42 extendssubstantially the entire length of drum 10 as best shown in FIGURE 1,with the left and right ends being closed by means of end plates orbafiles 50 and 52 respectively. These end plates help enclose the areajust above the downcomers 16, thereby forming an open topped tank withinthe drum 10. The end walls also aid in supporting the bafile 42. Thebaifie 42 has cut out portions 43 along the length thereof toaccommodate the passage of pipes 22, as shown in FIGURE 1. Asillustrated in FIGURE 2, the drum 10 is provided with an end man holecover opening 46 to permit access to the drum internal.

Pipe 14 is provided with a plurality of openings 44 along the lengththereof through which the feedwater is discharged into the drum. Asillustrated, these openings direct the feedwater towards the area justabove downcomers 16, at approximately a 45 angle from the vertical. Inthis manner, the relatively cool feedwater is confined within theportion of drum 10 above the downcomers 16, thus preventing to a greatextent condensation within the drum, and more importantly, allows coolerwater to flow through the downcomers, thus increasing circulation.

As mentioned previously, the baffle construction and the position ofopenings 44 in the pipe 14 so as to direct the incoming feedwatertowards the wall containing downcomers 16 results in a more stable waterlevel within the drum, regardless of changes in load. This arrangementalso increases the velocity of flow through the natural circulationsystem consisting of downcomers 16 and risers 18.

It is to be understood that the above description is intended for thepurpose of illustration only and that modifications such as will occurto those skilled in the art are possible and are embraced within thescope and spirit of the invention. For example, all of the rows ofdowncomers 16 need not be positioned within the area confined by thebaffie, if desired. The number of downcomer rows to be included underthe segregating baffle can be varied depending on the heat transferredto these rows, the temperature of the feedwater as it enters the drum,the amount of boiler water recirculated at saturation temperature, andother related factors. Not only is the invention applicable to singleupper drum boilers, but to all multiple drum boilers and to allconvection bank boilers.

What I claim is:

In combination, a cylindrical drum adapted to house steam and water atvery high temperatures, riser tubes having open ends extending throughone side of the drum through which a mixture of water and steam isdischarged into the drum, separating means for separating the steam fromthe water that is discharged into said drum through said riser tubes,openings in said separating means through which the separated waterflows to the bottom of the drum, housing means enclosing all of theriser tube ends and connecting them to the separating means, an outletin the upper portion of said drum through which steam is discharged,downcomer tubes through which water flows from said drum connected tothe side of said drum opposite the connection of said riser tubes, afeedwater pipe extending parallel to the axis of said cylindrical drumabove said downcomer tubes, said feedwater pipe containing openingsalong its length to allow feedwater, at a lower temperature than thetemperature of the steam and water within said drum, to enter said drum,a substantially vertical baille means extending from the bottom of saiddrum to a point near the water level therein but above the position ofsaid feedwater pipe, said baffie means in conjunction with a portion ofthe drum forming an open topped tank within said drum, said open toppedtank enclosing all of said downcomer tubes and all of said openings insaid feedwater pipe, and said openings in said feedwater pipe beingpositioned such that the incoming feedwater is directed away from saidone side of said drum containing the riser tube connections, the greaterportion of the comparatively cooler incoming feedwater being entrappedwithin the open topped tank portion of said drum, and thus flowing fromsaid drum through said downcomer tubes before substantially mixing witha major portion of the separated water from the separating means.

References Cited in the file of this patent UNITED STATES PATENTS2,264,248 Schrader Nov. 25, 1941 2,594,490 Patterson Apr. 29, 19522,743,709 Armacost May 1, 1956 2,763,245 Place Sept. 18, 1956 2,954,014Rehm Sept. 27, 1960

